"Mike's changed a lot over the course of the season," Tveit says on a recent visit to the The Hollywood Reporter offices. "Everyone kind of gives him a hard time when he first gets out there about being the new guy, even though from my standpoint I didn't always believe that; I thought I was putting it on a little bit for them."

But as time went on, Mike's investigation into his mentor Briggs (Daniel Sunjata) and the dangerous situations he was at the center of as an undercover agent toughened up the book-smart Quantico graduate.

"He's really thrown into the situation where he may have all the books marked in the world, but he needs to learn how to work in the field. He's gone through a lot of tough stuff over the course of the season, so he's definitely changed by that," Tveit says.

As Tveit tells it, the undercover agents' "moral ambiguity" and their "ability to justify letting some stuff that's even criminal go to get to the bigger goal" was a key trait Mike realized he was "good" at. "That's a surprise to him," he says.

Portraying an FBI guy on TV made Tveit appreciate the real-life agents whose lives are constantly in jeopardy. "It's tough stuff," he says. "They're out there on our behalf and trying to make the world a better place...These guys are in the line of fire, in the face of danger. One wrong move, one bad day can literally get them killed."

How the season wraps up Sept. 12 is "interesting," Tveit hints. "I think Mike -- what he wants for himself is changing a little bit. Maybe he thinks the field agent thing, he's actually good at. Maybe he will do that for a little while longer before jumping out of there."